In a wireless communication system using radio frequency identification (RFID) technology, when an antenna included in a data carrier receives a carrier wave transmitted from an antenna included in a reader/writer, an electromotive force is induced by electromagnetic induction. Then, a rectifier circuit included in the data carrier generates direct current from alternating current induced in the antenna.
In general, a rectifier circuit included in a data carrier includes a so-called diode-connected MOS transistor (hereinafter referred to as a “transistor”) in which a gate is connected to a source or a drain. The rectifier circuit rectifies an AC signal to a DC signal.
In order to prevent breakdown of the diode-connected transistor included in the rectifier circuit, peak reverse voltage that is approximately three times as high as AC voltage to be rectified is needed. Here, the level of AC voltage input to the rectifier circuit included in the data carrier varies depending on the distance between the antenna of the reader/writer and the antenna of the data carrier. Therefore, it is necessary to select a transistor to be used in consideration of the maximum AC voltage input to the rectifier circuit.
FIG. 2 is a graph showing reverse-bias static characteristics of diode-connected transistors (whose channel formation regions are formed using polysilicon and off-state current is 10−9 A/μm) included in a rectifier circuit. Note that the horizontal axis represents voltage [V] and the vertical axis represents current [A]. According to the graph, when a reverse bias is applied to the diode-connected transistors, a breakdown phenomenon occurs with voltages of higher than −10 V and the transistors are broken.
Reverse current which flows in a reverse-bias state correlates with off-state current of the diode-connected transistor. A free electron in the reverse current is accelerated by an electric field and causes collisional ionization; thus, the breakdown phenomenon occurs.
Therefore, it is important to use a transistor whose off-state current is small as the diode-connected transistor included in the rectifier circuit in order to prevent breakdown of the transistor and increase reliability of the rectifier circuit.
By the way, it is known that a transistor in which an oxide semiconductor is used for a channel formation region has small off-state current.
In Non-Patent Document 1, a rectifier circuit including a transistor in which an oxide semiconductor is used for a channel formation region is proposed.